Doing calf raises with your legs straight builds more muscle in the back of your lower leg right after your workout than doing them with bent knees. In a study of young women, straight-leg raises increased muscle size by nearly 9%, while bent-leg raises actually caused a tiny decrease.

When young women do calf raises until they can't do any more, doing them with straight legs makes the upper calf muscle grow way more than doing them with bent knees (+8.8% vs -0.9%).

Doing calf raises with your legs straight causes your calf muscles to swell up much more right after the workout than doing them with bent knees. In a study of young women, straight-leg raises increased calf thickness by 14.5% right away, while bent-leg raises only increased it by 7.0%.

When young women do calf raises until they can't do any more, doing them with straight legs makes the outer calf muscle grow about twice as much as doing them with bent knees.

If you're a young woman doing calf raises, bending your knees while lifting will make your soleus calf muscle swell up more right after the workout than keeping your legs straight. This happens because the bent-knee position targets that specific muscle more intensely during the exercise.

Doing calf raises at the bottom part of the movement — where your calf is stretched — might build more calf muscle in young women than doing the full raise, according to this claim.